C band and Ku band Arctic Ocean sea ice backscatter maps at 40¿ incidence angle, produced from the ERS 2 active microwave instrument operating in scatterometer mode and Advanced Earth Observing System NASA scatterometers, respectively, are presented and compared. The noise level on these maps is estimated from the comparison of successive maps and is found comparable, although larger at C band than at Ku band. In both cases the relative noise level increases as backscatter level decreases. Backscatter shows a greater dynamic range at Ku band than at C band, going from first-year to multiyear ice; moreover, the Ku band to C band backscatter ratio varies considerably as a function of sea ice type. Surface thawing, in June, leads to a brutal decrease in backscatter in both frequency bands, as well as in the Ku band to C band ratio. The study of the time evolution of backscatter over five different regions of the Arctic Ocean demonstrates the influence of both advection and local evolution on this parameter. ¿ 1999 American Geophysical Union